This invention relates in general to fuel rails for use in the fuel delivery systems of engines. In particular, this invention relates to an improved method of manufacturing such a fuel rail using hydroforming techniques.
Most engines, such as internal combustion engines and diesel engines that are used in vehicles and other devices, are equipped with a system for delivering fuel from a source or reservoir to a plurality of combustion chambers provided within the engine. In most modern vehicular engines, this fuel delivery system is a fuel injection system, wherein fuel is supplied under pressure to and selectively injected within each of the combustion chambers of the engine for subsequent combustion.
To accomplish this, a typical fuel injection system includes one or more fluid conduits (typically referred to as fuel rails) that transmit the fuel from the source to each of the combustion chambers of the engine. Each of the fuel rails is typically embodied as a hollow tube including an open end, a closed end, and a plurality of nodes located between the open and closed ends that extend outwardly from the hollow tube. The open end of the fuel rail is adapted to communicate with the source of the fuel. The hollow tube is shaped such that each of the nodes is positioned directly adjacent to an inlet of an associated one of the combustion chambers of the engine. Each of the nodes usually terminates in a hollow cylindrical cup portion that is adapted to receive a fuel injector therein. The fuel injectors are typically embodied as solenoid controlled valves that are selectively opened and closed by an electronic controller for the engine. When opened, the fuel injectors permit the pressurized fuel to flow from the fuel rail into the associated combustion chamber. When closed, the fuel injectors prevent fuel from flowing from the fuel rail into the associated combustion chamber. By carefully controlling the opening and closing of the fuel injectors, precisely determined amounts of the pressurized fuel can be injected from the fuel rail into each of the combustion chambers at precisely determined intervals.
Typically, the fuel rails are formed from a rigid material, such as plastic or metallic material. Plastic material fuel rails can be formed by injection molding and other well known processes. However, the majority of fuel rails are manufactured from metallic materials. Typically, a metallic fuel rail is manufactured by initially providing a tubular body portion that is bent or otherwise deformed to a desired shape. Then, a plurality of openings are formed through the hollow body portion at the locations where it is desired to provide the above-mentioned nodes. A hollow node portion (typically having the cup portion already formed therein) is next positioned adjacent to each of the openings and secured thereto, such as by brazing.
Although the above-described method for manufacturing the fuel rail has been performed successfully for many years, several drawbacks have been noted. One of such drawbacks is that it is relatively difficult to insure that the node portions of the fuel rail are precisely located relative to the body portion. This is because of several reasons. First, a relatively complicated fixture must be provided to precisely support the body portion and each of the node portions until they are secured together. Second, because the brazing process involves the application of relatively high temperature heat, dimensional stability in the precise positioning of the nodes is difficult to control. Thus, it would be desirable to provide an improved method of manufacturing a fuel rail that avoids these drawbacks.
This invention relates to an improved method of manufacturing a fuel rail for use in a fuel delivery system for an engine, such as is commonly used in a vehicle. A hydroforming apparatus includes first and second die sections having one or more retractable mandrels provided in respective bores. A workpiece is disposed within a die cavity defined by the first and second die sections, and end cylinders are moved into engagement with the opposite ends thereof. A pair of pressure feed pistons are disposed within the interior of the workpiece. The pressure feed pistons include respective head portions that sealingly engage the inner surface of the workpiece to define a pressure chamber within a central portion thereof. One of the mandrels is retracted position within its bore such that the inner surface thereof is disposed outwardly from the surface of the recess formed in the second die section. Either during or after such retracting movement, pressurized fluid from the source is introduced into the pressure chamber defined between the head portions of the pressure feed pistons. As a result, the portion of the workpiece that is exposed to such pressurized fluid is deformed outwardly into conformance with the portion of the die cavity located within the pressure chamber, including the portion of the bore that is exposed when the mandrel is moved to the retracted position. Accordingly, an outwardly extending node blank is formed on the workpiece. Thereafter, the pressure feed pistons are moved outwardly apart from one another to respective second positions that re-define the pressure chamber within the workpiece in a somewhat larger manner. Thus, the head portions of the pressure feed pistons are located outside of other bores formed through the second die section. The other mandrels are moved to their retracted positions within their respective bores, and pressurized fluid from the source is again introduced into the enlarged pressure chamber defined between the head portions of the pressure feed pistons. As a result, the other portions of the workpiece are deformed to form additional outwardly extending node blanks on the workpiece. To complete the manufacturing process, the deformed workpiece is removed from the hydroforming apparatus and subjected to conventional machining and/or metal working operations to provide a finished fuel rail.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.